Microprocessor controllers have impacted the electronics industry in as big a way as the transistor did 25 years ago. Today's state of the art 32 bit microprocessors evolved from a four bit integrated circuit which, at its conception, was believed to have limited usefulness. The variety of uses for the microprocessor controller however, has expanded at least as quickly as the performance capabilities of the microprocessor hardware.
A typical microprocessor controller system includes hardware for performing a control function, hardware to allow a user and/or other computers to interface with the microprocessor, and software for controlling operation of the system. Some typical interfaces to the microprocessor system are cathode ray screens, keyboard interfaces, and printers. One use of the controller system may be to monitor various conditions and apprise the user and/or other hardware of the existence of certain status conditions as those conditions are sensed.
A special form of a microprocessor known as a speech synthesizer is a rather sophisticated output device gaining popularity for certain uses. The speech synthesizer can generate messages almost indistinguishable from the human voice. Speech synthesizers have added flexibility and user friendliness to a variety of controller applications such as computer aided instruction and robotics.
A variety of literature sources describe the functioning of these special function microprocessors. There are a number of different techniques in generating artificial speech. So-called "format synthesis" is an electronic modeling of the human vocal track. One specific form of the format technique is called phoneme synthesis where messages are formed from basic sound units that make up words. Each phoneme is given a numeric code and the synthesizer circuit utters these sounds corresponding to the codes when it is activated by a controller. Words and sentences are assembled by stringing together the phonemes. The electronic voice generated in this manner is very flexible since any message can be built up using an appropriate grouping of phonemes.
A second speech synthesis technique is so-called wave form digitization where actual recordings of messages are digitized and stored so that they may be reproduced electronically. The quality of speech in this second technique tends to be better than the phoneme procedure. The drawback to this wave form digitization procedure is that fairly large amounts of memory must be utilized to store the digitized messages. Since each message must be stored, the digitization process is much less flexible than the phoneme synthesis.
Each of the multiple speech synthesizers commercially available includes a text-to-speech algorithm that accepts a control input and performs a synthesis. The program or algorithm used in controlling this process varies in length depending upon the type of speech synthesizer and the quality of speech provided. As a rule of thumb, however, the longer the control algorithm for the speech synthesizer, the better the voice quality from the output of that unit.
Industrial and consumer product uses of speech synthesis are known. An audible message is used for either instructing a user or apprising the user of the status of the system. Speech synthesizers have been used, for example, in an automobile to apprise the motorist of the condition of the automobile. A voice-like message tells the motorist that his seat belts remain unbuckled after he has entered the car and placed his key in the ignition. Use of the speech synthesizer for automobile status warnings have also been used to apprise the user when his automobile has a problem that needs attention.
A typical auto monitoring environment is hot, dirty, and filled with spurious signals from a number of sources. In such an environment, the reliability of the speech synthesizer is placed in jeopardy unless special precautions are taken. As a corollary to this concern, as the complexity of the speech synthesizer system is expanded, the sources of malfunction in such a system also increase.
As speech synthesizer expand their capabilities and as the quality of their voice synthesis improves, such circuits will undoubtedly find other applications in environments equally as hazardous to these systems. Reliability, quality and flexibility are attributes which any speech synthesizing system must exhibit if it is to be used in more than an experimental curiosity used only in tightly controlled environments.